Documentation: PCI: Add PCI endpoint NTB function user guide

Add documentation to help users use pci-epf-ntb function driver and
existing host side NTB infrastructure for NTB functionality.

[bhelgaas: fix a few typos]
Link: https://lore.kernel.org/r/20210201195809.7342-18-kishon@ti.com
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>

2 files changed, 162 insertions, 0 deletions

diff --git a/Documentation/PCI/endpoint/index.rst b/Documentation/PCI/endpoint/index.rst
index 9cb6e5f3c4d5..38ea1f604b6d 100644
--- a/Documentation/PCI/endpoint/index.rst
+++ b/Documentation/PCI/endpoint/index.rst
@@ -12,6 +12,7 @@ PCI Endpoint Framework
    pci-test-function
    pci-test-howto
    pci-ntb-function
+   pci-ntb-howto
 
    function/binding/pci-test
    function/binding/pci-ntb
diff --git a/Documentation/PCI/endpoint/pci-ntb-howto.rst b/Documentation/PCI/endpoint/pci-ntb-howto.rst
new file mode 100644
index 000000000000..1884bf29caba
--- /dev/null
+++ b/Documentation/PCI/endpoint/pci-ntb-howto.rst
@@ -0,0 +1,161 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================================================
+PCI Non-Transparent Bridge (NTB) Endpoint Function (EPF) User Guide
+===================================================================
+
+:Author: Kishon Vijay Abraham I <kishon@ti.com>
+
+This document is a guide to help users use pci-epf-ntb function driver
+and ntb_hw_epf host driver for NTB functionality. The list of steps to
+be followed in the host side and EP side is given below. For the hardware
+configuration and internals of NTB using configurable endpoints see
+Documentation/PCI/endpoint/pci-ntb-function.rst
+
+Endpoint Device
+===============
+
+Endpoint Controller Devices
+---------------------------
+
+For implementing NTB functionality at least two endpoint controller devices
+are required.
+
+To find the list of endpoint controller devices in the system::
+
+	# ls /sys/class/pci_epc/
+	2900000.pcie-ep  2910000.pcie-ep
+
+If PCI_ENDPOINT_CONFIGFS is enabled::
+
+	# ls /sys/kernel/config/pci_ep/controllers
+	2900000.pcie-ep  2910000.pcie-ep
+
+
+Endpoint Function Drivers
+-------------------------
+
+To find the list of endpoint function drivers in the system::
+
+	# ls /sys/bus/pci-epf/drivers
+	pci_epf_ntb   pci_epf_ntb
+
+If PCI_ENDPOINT_CONFIGFS is enabled::
+
+	# ls /sys/kernel/config/pci_ep/functions
+	pci_epf_ntb   pci_epf_ntb
+
+
+Creating pci-epf-ntb Device
+----------------------------
+
+PCI endpoint function device can be created using the configfs. To create
+pci-epf-ntb device, the following commands can be used::
+
+	# mount -t configfs none /sys/kernel/config
+	# cd /sys/kernel/config/pci_ep/
+	# mkdir functions/pci_epf_ntb/func1
+
+The "mkdir func1" above creates the pci-epf-ntb function device that will
+be probed by pci_epf_ntb driver.
+
+The PCI endpoint framework populates the directory with the following
+configurable fields::
+
+	# ls functions/pci_epf_ntb/func1
+	baseclass_code    deviceid          msi_interrupts    pci-epf-ntb.0
+	progif_code       secondary         subsys_id         vendorid
+	cache_line_size   interrupt_pin     msix_interrupts   primary
+	revid             subclass_code     subsys_vendor_id
+
+The PCI endpoint function driver populates these entries with default values
+when the device is bound to the driver. The pci-epf-ntb driver populates
+vendorid with 0xffff and interrupt_pin with 0x0001::
+
+	# cat functions/pci_epf_ntb/func1/vendorid
+	0xffff
+	# cat functions/pci_epf_ntb/func1/interrupt_pin
+	0x0001
+
+
+Configuring pci-epf-ntb Device
+-------------------------------
+
+The user can configure the pci-epf-ntb device using its configfs entry. In order
+to change the vendorid and the deviceid, the following
+commands can be used::
+
+	# echo 0x104c > functions/pci_epf_ntb/func1/vendorid
+	# echo 0xb00d > functions/pci_epf_ntb/func1/deviceid
+
+In order to configure NTB specific attributes, a new sub-directory to func1
+should be created::
+
+	# mkdir functions/pci_epf_ntb/func1/pci_epf_ntb.0/
+
+The NTB function driver will populate this directory with various attributes
+that can be configured by the user::
+
+	# ls functions/pci_epf_ntb/func1/pci_epf_ntb.0/
+	db_count    mw1         mw2         mw3         mw4         num_mws
+	spad_count
+
+A sample configuration for NTB function is given below::
+
+	# echo 4 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/db_count
+	# echo 128 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/spad_count
+	# echo 2 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/num_mws
+	# echo 0x100000 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/mw1
+	# echo 0x100000 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/mw2
+
+Binding pci-epf-ntb Device to EP Controller
+--------------------------------------------
+
+NTB function device should be attached to two PCI endpoint controllers
+connected to the two hosts. Use the 'primary' and 'secondary' entries
+inside NTB function device to attach one PCI endpoint controller to
+primary interface and the other PCI endpoint controller to the secondary
+interface::
+
+	# ln -s controllers/2900000.pcie-ep/ functions/pci-epf-ntb/func1/primary
+	# ln -s controllers/2910000.pcie-ep/ functions/pci-epf-ntb/func1/secondary
+
+Once the above step is completed, both the PCI endpoint controllers are ready to
+establish a link with the host.
+
+
+Start the Link
+--------------
+
+In order for the endpoint device to establish a link with the host, the _start_
+field should be populated with '1'. For NTB, both the PCI endpoint controllers
+should establish link with the host::
+
+	# echo 1 > controllers/2900000.pcie-ep/start
+	# echo 1 > controllers/2910000.pcie-ep/start
+
+
+RootComplex Device
+==================
+
+lspci Output
+------------
+
+Note that the devices listed here correspond to the values populated in
+"Creating pci-epf-ntb Device" section above::
+
+	# lspci
+	0000:00:00.0 PCI bridge: Texas Instruments Device b00d
+	0000:01:00.0 RAM memory: Texas Instruments Device b00d
+
+
+Using ntb_hw_epf Device
+-----------------------
+
+The host side software follows the standard NTB software architecture in Linux.
+All the existing client side NTB utilities like NTB Transport Client and NTB
+Netdev, NTB Ping Pong Test Client and NTB Tool Test Client can be used with NTB
+function device.
+
+For more information on NTB see
+:doc:`Non-Transparent Bridge <../../driver-api/ntb>`